The present invention relates to a magnetic card comprising a card substrate and a magnetic layer provided thereon for magnetic recording of information in a machine-readable fashion.
Having on a card substrate a magnetic layer for magnetic recording of an ID number or other data attributable to a card's user in a machine-readable fashion, magnetic cards are now widely used in the form of cash cards or credit cards.
So far, the security of magnetic cards has been enhanced by concealment of magnetic layers from view. As well known in the art, the aesthetic property and ability to prevent forgery of a magnetic card are improved by provision of a concealment printed layer or a hologram layer on the magnetic layer. One such known magnetic card
has a multilayer structure that has a magnetic layer, an underlying concealment thin-film layer formed of a metal or a metal compound, a printed layer and a hologram layer provided successively on a card substrate, so that information can be recorded onto the magnetic layer from the surface of the volume hologram laid on it and the information recorded on the magnetic layer can be read (JP-A 10-198950).
Among holograms known in the art, there is a relief hologram that may be formed of a thin film but has some difficulty in achieving three-dimensional appearances, and so conversion of the relief hologram to a volume hologram is now in the making. A volume hologram layer has a good stereoscopic effect, and enables a hologram to be recorded by a multiplicity of interference fringes parallel with its surface in a depth direction. A significant feature (redundancy) of the volume hologram layer is that even when more or less shaved away in the depthwise direction due to slide contact with a magnetic head, the same image can be reconstructed although its brightness drops.
However, the volume hologram layer is very soft, offering a wear resistance problem with slide contact with a magnetic head for machine reading, even when a protective layer is provided over the surface thereof. Usually, it is extremely difficult to form volume hologram layers in a thin-film state. For this reason, when the volume hologram layer is laminated on a magnetic stripe, spacing losses become heavy upon reading of magnetic information, rendering precise writing or reading of magnetic recording data difficult.
An object of the present invention is to provide a magnetic card having a volume hologram layer on its surface, which has improved wear resistance to sliding contact with a magnetic head, and ensures precise writing or reading of magnetic recording data, with much more improved ability to prevent forgery.